Optimising the Structure of Metal-Insulator-Metal Diodes for Rectenna Applications

Abstract

The work in this thesis investigates the design and fabrication of metal-insulator-metal (MIM) diodes using an ultrathin organic insulator. The organic insulating layer was found to be compact, highly conformal, and uniform, effectively overcoming the main design challenge in MIM diodes. The fabricated diodes have strong nonlinear current-voltage characteristics with a zero-bias curvature coefficient and a voltage responsivity among the best values reported in the available literature. The fabrication process is simple and carried out at low temperature, which is cost effective, and can potentially be ported to large-area roll-to-roll manufacturing. An encapsulation method to prevent MIM junctions’ degradation has also been developed.
Following the successful production of these MIM devices on a rigid substrate, with the fabrication only requiring low-temperature processing, the diodes were successfully fabricated on a flexible substrate with results similar to those fabricated on a rigid substrate. The flexible substrate diodes show no significant degradation in performance when stressed in a one-off bending experiment, although extreme mechanical stress testing does produce some loss in quality.
Also, an elegant method for matching the impedance of an antenna to that of a MIM diode was successfully developed, for optimal external conversion efficiency where the diodes are used in a rectenna device. The responsivity of the impedance-matched rectenna is approaching an order of magnitude higher than that of a control device without a matching network. The fabrication, electrical characterisation and physical analysis of both the MIM diodes and rectennas are discussed in detail in this thesis.